At present most thermal energy is being derived from the earth's natural resources such as petroleum, coal, and nuclear fuels. In recent years, the realization that these natural resources are limited has led to programs for harnessing sunlight as a source of thermal energy.
The utilization of sunlight requires development of an agent capable of effectively storing the heat of sunlight.
It has been known to the art that norbornadiene represented by the following formula is useful as an organic heat-storing agent. ##STR1## [Refer, for example, to Organic Syntheses 51, 133 (1971); R. R. Hautala, J. Little and E. Sweet, Solar Energy 19, 503 (1977).]
Norbornadiene, on exposure to light, is isomerized to quadricyclene represented by the following formula. ##STR2##
During this exposure, the energy of the sunlight is stored in the form of thermal energy. When quadricyclene is reverted to norbornadiene, thermal energy is liberated at the rate of 88 kJ per mole of quadricyclene.
The inventors have confirmed that 7-substituted norbornadienes produced by substituting a hydroxyl group, an acyloxy group, any of the alkyloxy groups, etc. for one of the hydrogen atoms attached to the 7 position of norbornadiene similarly function as organic heat storing agents.
The storage of heat during the isomerization of norbornadienes through irradiation with sunlight into corresponding quadricyclenes and the liberation of heat during the reverse of the isomerization, therefore, make it possible to utilize sunlight.
The aforementioned norbornadienes, however, tend to undergo photopolymerization in the presence of oxygen, have high volatility, undergo heavy loss during repeated use, and emit offensive odor. Because of these and other drawbacks, practical use of norbornadienes as heat storing agents poses many problems yet to be solved.
An object of this invention is to provide a method for the manufacture of a heat storing agent capable of storing light energy such as the energy of sunlight as thermal energy without entailing the drawbacks suffered by the aforementioned norbornadienes.